This invention relates to a bichromatic optical cell capable of detecting an object either by interruption of a reflection caused by a reflector, without utilizing the angle of incidence of the received beam, in a mode called a reflex mode, or by reflection onto an object utilizing a variation in the angle of incidence of the received beam,xe2x80x94by a triangulation effectxe2x80x94, in a mode called a proximity mode.
Depending on the distance of the object to be detected, its brightness or its color or indeed local detection conditions, it is desirable to use a reflex cell in certain cases, and a proximity cell in other cases. The usual cells designed to function in reflex mode are not able to function in proximity mode and vice versa.
Nevertheless, in document EP-329 083, a bichromatic cell with a broad detection ability has been proposed. This cell, in cases of red and infrared emissions, is combined with a special reflector that absorbs the infrared, and comprises a special receiver component with two photodiodes, one dedicated to the red light and the other to the infrared light. A bichromatic cell has also been envisaged that allows one to detect bright objects only in the reflex mode (document FR-2 442 457). Apart from this disadvantage of not being able to operate in proximity mode, such a cell requires a specific reflector in order to eliminate one of the wavelengths. Such special reflectors are expensive.
An objective of the invention is to provide a photoelectric cell capable of operating in reflex mode or in proximity mode, through inexpensive and efficient means that notably exclude the need for a specific reflector.
The invention relates to a photoelectric cell comprising two emitters capable respectively of generating a first beam and a second beam of different wavelengths, and a receiver arranged in a manner to receive, at a fixed or a variable angle of incidence, a beam able to be influenced by an object, from one or other emitter.
According to the invention, the photoelectric cell comprises means of polarizing the first beam, the receiver and the cell being fitted with means of selecting a first operating mode, notably of the polarized reflex type, or a second operating mode, notably of the proximity type, which activates one or other of the emitters depending on the mode selected.
Preferably, the receiver has at least two output channels connected to a processing circuit and capable of supplying respective signals the ratio of which varies according to a monotone function of the distance of the object, while the means of operational selection are capable of blocking one or other of the output channels from the receiver and/or of configuring an active optical receiving area of the receiver. The selection of the operating mode of the cell can be carried out automatically or in a manual way.
A non-limitative embodiment of the invention will now be described below, making reference to the appended drawing.